What elements affect the PUE value of the data center

PUE is not greater than 1.4 in air conditioning technology is feasible. Constraints on PUE, I think, at this stage is mainly cooling technology, air conditioning technology, how to efficiently remove heat. Post a Tsinghua University academician Jiang Yi's speech: Good morning, guests, experts and leaders! I seem to be the first time to participate in the green data center technology conference, because we are not engaged in the computer industry, is engaged in air conditioning, engaged in building energy efficiency, but it seems that we are slowly pushed into this industry. Why? It is because the energy consumption of air conditioning or the energy consumption of sending heat and cooling in the data center accounted for a relatively large proportion. So, just now I heard the front of this leader said that data centers are almost to the extent that the operation of this degree, the operation of the main energy consumption, energy consumption in 40% or more is the energy consumption of air conditioning. Therefore, how can we reduce the energy consumption of air conditioning, on the one hand, to contribute to the country's energy saving and emission reduction, on the one hand, but also to enable us to produce better economic benefits of the data industry, has become an important issue, so I'm with you today to report on our ideas and experience in this regard.　From the point of view of the characteristics of the air conditioner, now with the development of computer electronics technology, chip technology are higher than the original, the host's heating degree is getting bigger and bigger, which leads to the air conditioning heat exhaust to become a big part of this. Behind there are some fine development of the situation is not to say, directly see the air conditioning in the head. Now the general results of statistics, for small and medium-sized data centers are probably PUE value of 2, or more, which is the air conditioning accounted for half or more of an energy consumption. For large IDC server room management to do a better job, this time the air conditioning efficiency is relatively high, but can also account for about 40% of energy consumption.　Therefore, to reduce the energy consumption of the data center may be a way to improve the efficiency of the use of servers, no work to let it rest, on the one hand, to reduce the energy consumption of air operation, of course, the power supply also has the technology can be improved. Air conditioning should have a lot of potential, air conditioning inside the energy consumption consists of what? In the past, I want to say that the refrigeration machine, the compressor consumes more power, in fact, the compressor consumes power in 50% -60% or so, in addition to the compressor, the fan can also be accounted for in 40% or more of the air-conditioning energy consumption.　What is the situation now? There are probably so many pieces: First, because of year-round refrigeration, so the vast majority of data centers cooling machines are open, this is the total air conditioning over the year, the test point situation, you can see that the winter, summer difference is very little, Beijing, Shanghai, Guangzhou, cold places, the difference between the hot place is very little, it should be said that the winter days are cooler, the air conditioning in Beijing is getting more and more substantial down, this change is not very big, so the whole year is used here. Then, about the heat density is very large, responsible for these heat exhaust, so the circulation wind is particularly large. And the wind blowing is also very strong, not to reduce the air volume, reduce the temperature of the air supply, but when the temperature of the cold source is lower than the temperature of the house, the evaporator condensation, hate every day out of the wet, out of the wet and afraid of the house is too dry, so there are some humidifiers, this side of the dehumidification, the other side of the humidification, but also to use electricity, the cold days of winter but also to refrigeration, which constitutes the current data center, whether it is a large, or a small Air conditioning energy consumption is high, the main problem.　This is a bad thing, but on the other hand, it's a good thing. It shows that we have a lot of potential here, a lot of potential to reduce air conditioning energy consumption. So, which way to go? How? Once I heard that this air conditioning and your building energy efficiency is the same thing, building energy efficiency to grasp the envelope insulation, we whole this, the envelope, the effect is very small, or no effect, why? Because an IDC dense a little bit of server room a square meter of heat production of about 3-5 million, through the envelope into or out of the heat will not be more than folded in the footprint will not be more than 50 watts, so the impact of the envelope is very small, that is, 1%, 2% of the impact. Of course, through some technology, to avoid direct solar radiation on the facade, than to come to me here hot, and then take the sun to shine on me, as much as possible, airtight, don't let the wind come in, this is very important. Some experts may say, wind seepage, what's wrong, if the house is not airtight, is uncontrollable outdoor seepage of wind, is cool, but the humidity drops, summer heat container is not good, and because of the humidity outside the big changes in humidity, I hope that the humidity inside the data center to maintain the basic stability of unchanged, to me to add humidity, dehumidification of the troublesome thing. Therefore, the house should be made airtight through various aspects, and it is not a matter of heat preservation for the present, and airtightness is the most important thing.　Then, how to get the heat out, immediately a few years ago, some companies want to think of ways to say that since the winter does not open the refrigeration machine, and outside the cool, the simplest ventilation, it is through the cool air into the heat exhaust, which is a little energy-saving, but I'm afraid that the data center to do so is not very appropriate, why? Outdoor dust spoils, the machine must be clean, humidity outdoor is changing, a cubic meter of air in Beijing in the summer there are 2 grams of water vapor, in addition, China is a coal-burning countries, 70% of the fossil energy come from coal, coal combustion out of sulfur, sulfide to the indoor, will lead to corrosion of the surface phenomenon, so this is not good, your cooling system is a service for the host, if it is detrimental to the host, whether it is dust or sulfur, and humidity will affect the host. If there is damage to the host, whether it is dust or sulfide, and humidity will affect the life of the host, which is absolutely can not have. Therefore, said the idea of eliminating dust through filtration, the idea of humidification, dehumidification to change the humidity, the idea of desulfurization, when all of these things on the shelf, it was found that the cost of investment and energy consumption is not low, and maintenance and management of the workload immediately went up, then so large data centers require high-reliability operation, and so this is a little twisted.　There is a heat exchange through the cool air back, this idea is quite good, for some small-scale computing centers, like a building in the data center can sometimes, but for large-scale server room is not possible to achieve, is because the direct air ducts to go so much heat to have how much air volume directly outdoor back and forth to change the air, the volume of the air ducts there is not suitable, and then the maintenance of the workload is very large, especially the stolen goods. The air ducts are not suitable, and then the maintenance workload is very large, especially the spoils. Therefore, the outdoor low temperature must be used on the idea, is through the outdoor fresh air, how to cool down through some kind of energy, and finally the machine inside the heat away.　Therefore, the entire data center air conditioning and our building air conditioning concept is not the same, it is the core of the matter is how to chip out of the heat through some kind of medium heat transfer, after the transfer, a few exchanges, and finally led to the outdoors on such a task. Therefore, the fundamental goal at this time is to let the chip temperature does not exceed the standard temperature, and then the temperature discharge. So that the chip surface temperature and cold source temperature difference with the thermal resistance is proportional to the equivalent thermal resistance, that is, how to reduce the core of this equivalent thermal resistance has become such a problem. Temperature difference is small is if I chip temperature is not allowed to exceed 40 degrees, if my temperature difference is 20 degrees, as long as the outdoor temperature is lower than 20 degrees, I do not have to open the cold air can be discharged heat, so we need to reduce the equivalent thermal resistance. So, what does this equivalent thermal resistance consist of? Found like one of our Chinese complex, three resistors, three equivalent thermal resistance, which three processes? One is the heat transfer link between the chip and the air, the greater the difference, the greater the temperature difference, for example, I can take the average temperature, the equivalent thermal resistance is this area divided by the heat, the first link is the container and the chip surface heat transfer link. The second link, for example, I have a precision air conditioning and water, or outdoor cold water heat transfer, this cold water and the container between the heat transfer link, we call the transport and heat transfer thermal resistance. The third link, circulating medium and the cold source of air exchange, called the cold source of heat transfer thermal resistance. For example, the indoor temperature to 20 degrees, the actual only owe 10 degrees of temperature difference, this time the cold air machine to provide the work is this 10 degrees of temperature difference. Therefore, the thermal resistance is reduced, either with a natural cold source or open chiller can reduce power consumption. So, the core issue is to bring down the thermal resistance of these three links. So, on the three keys, first, reduce the thermal resistance of the heat collection process, while not increasing the fan power consumption. Second, reduce the thermal resistance of the heat transfer process, while not increasing the transmission power consumption. Third, find a lower temperature natural cold source, but do not damage the environment.　Look at the following article by article, the collection process of thermal resistance, the actual collection of thermal resistance, in addition to the air and the chip heat transfer, there is still a considerable consumption of cold air inside the room with the hot air mixed with each other, refrigeration is to separate the cold air hot temperature, separated from the hot and cold air, the house and no place to run, and mixed up, so to avoid mixing of cold air and hot air. For example, if a given chip temperature, when the mixing is small, the return air temperature can be tighter close to the chip, if I constant chip temperature back to the air less, so you can make greater use of this resource. There are some measured data, is measured in the large IC room, we can see, for example, the cold channel to come in, from the room should be sent out here is 16 degrees, to here how can more than 30 degrees? There is still a block on top of it, where does this 30 degrees come from? It is because after part of the server, there is a gap inside the server, and the hot air from the gap seeps back, and the hot air mixes with these things to these places, and it can reach 35 degrees. In order to ensure that the effect of these servers above, so we have to reduce the temperature of the air supply, in order to ensure that the above almost, the results of the temperature difference will be stretched, resulting in an increase in the entire cold cross heat. So, here look at the exhaust air has 40 degrees, these exhaust air 35, 36 degrees, the total to the air conditioning under a look, the temperature of the air distribution is only 28 degrees, how to reduce it? It is the cool air in the past with the hot air mixed up, so the chip is probably more than 45 degrees. If you avoid these mixing, you can easily increase the return air temperature to 35 degrees, the delivery temperature can also be increased to 20 degrees, to maintain the highest temperature of the chip temperature remains unchanged, so the temperature difference is much smaller, the collection of equivalent thermal resistance down. Of course, the specific calculation can be taken out of the temperature difference carefully calculated to know what is wrong, the general guideline is this. So, in the top of the cabinet rack some baffles, so that can be somewhat improved. However, because of the unavoidable airflow short-circuit phenomenon between the blade servers within the Jin Gui, there is still a short-circuit phenomenon, so that there is a by-pass of incoming hot airflow in the cold air flow path, and there is a by-pass of incoming cold airflow in the hot air flow path.　There is also a direct heat exchanger installed in the cabinet, in the cabinet or cabinet next to the preparation of cold air, can effectively reduce the mixing of such a phenomenon, reduce the heat collection process temperature difference, you can reduce the amount of air, abundance, and significantly reduce the fan power consumption. Therefore, this is a very important article, but not let the cabinet out of the water.　So that there is a practice, is the use of backplane cooling, the air conditioning system heat exchanger installed in the cabinet loaded with IT equipment, according to the various different cabinets in the machine room to achieve on-demand cooling, to avoid localized heat. The distributed cooling system brings the heat absorption end of the air conditioning system closer to the heat source. This is the first to reduce the thermal resistance in the heat extraction and collection process.　The second to reduce the thermal resistance in the transmission and distribution process, the actual this link such as a line of air conditioners, is the air and water heat transfer, then the air temperature is such and such, the water temperature, it will be seen that sometimes tend to are not balanced, is with the nature of the triangle, as long as with the nature of the triangle, a part of the waste of the temperature difference. So, the idea is to adjust the flow on both sides, so that the temperature difference between the two sides is close, you can effectively reduce the equivalent thermal resistance of the number of distribution system, or reduce the equivalent temperature difference. Sometimes said to be due to my use of the backplane, or the cabinet heat exchanger that is not going water, whether it is going carbon dioxide, or Freon, this is the cabinet to send the air temperature, this is the heat pipe temperature, this is the outdoor side of the temperature of the import and export, it is such a process, (as shown in the figure), there is also a kind of heat exchanger, each row of the heat pipe is connected individually, at this time, indoor and outdoor temperatures become much smaller, although the area of the heat transfer The same, it is much stronger. Of course, this will lead to a complex arrangement of heat pipes, but between the two, there is always a good trade-off to reduce the thermal resistance of the transport process or to reduce its temperature difference.　The third one is what kind of outdoor natural cooling source we use and how to combine this natural cooling source with my mechanical refrigeration organically and uniformly? Because sometimes it is hot but also have to open the cold machine, the two can not realize a more natural conversion? We now look at where the heat is actually discharged, the actual air is not a problem in the air, we have three temperatures, one is the dry-bulb temperature of the air, such as today's outdoor temperature of 27, 28 degrees, is the temperature of the weather forecast. Direct heat transfer is the dry bulb temperature. However, if I take the cooling tower outside to spray water, is the wet bulb temperature, about 23, 24 degrees. For example, by May 1, the wet bulb temperature is much lower than the dry bulb temperature, so through the cooling tower can reduce the wet bulb temperature, but also can not be lowered, there is a kind of indirect evaporative cooling, many places in the western region with it to do air conditioning, it can be asked to try to fall to the outdoor dew point temperature, such as now at this time, Beijing's dew point temperature is lower than 20 degrees.　This is to take the Beijing weather as an example, the blue is the global dry bulb temperature, the red is the wet bulb temperature, the green is the year-round dew point temperature change. So, if I think about the safety dew point temperature, the annual Beijing 5876 hours below 20 degrees of time accounted for 67% of the year, if the thermal resistance is done well, it is only 10% of the time, do not do a good job, 15 degrees of time, the dew point temperature can also account for 77% of the time. So that's still a pretty big percentage.　So how do you unify it with the chiller for a seamless, natural transition? This is a program, including several parts, first of all, the cabinet, just now I talk about the back plate heat transfer, now it is the top and bottom of the heat transfer, the air in the house 26 degrees, from here into the cabinet, two sets of heat exchangers, a group of one tube to 19 degrees, a tube to 16 degrees, after two kinds of heat transfer, from 26 degrees to 20 degrees, through the server that generates heat to 32 degrees, and then through the two heat exchangers to cool down, and then to 26 degrees, and then come back. And then back again, to maintain the temperature in the house is 26 degrees, not by the holes installed elsewhere in the house, but by this cabinet, the temperature in the house is determined by the cabinet, because the temperature in the house is 16 degrees, the dew point temperature is only 12, 13 degrees, I make the supplies airtight, and people do not really go in there, and there is no wet thing in there. Then, these four sets of heat exchangers, take the heat pipes and lead them out, and these four sets are 16, 19, 22, 25 degrees, and then this water is just exchanging heat with these heat pipes, bringing all the heat to the water, so it goes from 15 en degrees, up to 24 degrees. Then, 24 degrees, if the outdoor is two pipes, cold air without opening, directly through the indirect cooling tower will be able to drop the water temperature of 15 degrees, if the temperature is even lower, as long as the fan with the conversion device here, to maintain my access to the heat exchanger throughout the year only 15 degrees. When the outdoor temperature is as high as 30 degrees, the dew point temperature to 18 degrees, this time the cooling tower can still play a role, can start 1/3 of the cold still out of here, not enough and then take the chiller down part. Therefore, this chiller is continuous can make the cold air from 10% of the composite gradually added to 5% of the composite. Cooling tower as long as the dew point temperature is below 20 degrees, always starting point.　Such a system, here calculated, take Beijing's meteorological conditions can be seen, if it is such a room, with the general traditional room to compare, we will directly take it a year of electricity is 100 percent, then even if there is no natural cold source, that is, to take the chiller to do, but because I reduce the mixing, reduce the number of energy consumption, energy saving of 40% or so. If we use the best indirect cooling method, the power consumption is only 23%, can save 70% of the power, so there is a huge potential for energy saving.　Along these lines, we have some examples of machine room renovation, which is a Tsinghua University library of a whole university to support the entire academic teachers, students do research data center. It was originally in this room placed a bunch of air conditioners, more machines, the heat is still big, so add several air conditioners. With just this figure almost the same way, the results of the total cabinet inside the fan down to 7 kilowatts, this time the energy efficiency ratio from 2.7 to 8.2, only 1/3 of the original energy consumption. The hottest time, the chiller have to open, even so, energy consumption is still half the difference. So, the whole year down the total energy consumption can be reduced by 60% or so, this is a real case, there are still some regrets, that is, do not do thoroughly, do thoroughly, but also be able to further reduce the amount of consumption.　To sum up, the data center heat exhaust air conditioning actually has huge energy-saving potential and energy-saving space. It is the core of the airflow organization of the machine room how to collect heat reasonable air conditioner, which several basic principles, one is to avoid as much as possible different temperatures of the airflow admixture, we are now air conditioning cabinets for the purpose of refrigeration, not air conditioning refrigeration of the machine room, so as far as possible to the cold source of the closer the better the heat-generating body, make full use of the natural cold source, there are a variety of different laws to obtain different temperatures, and then ideas Introduction of energy consumption, so give out these ideas, a certain one or two practices today, the actual play under this idea of the spirit of innovation can also create a good variety of programs, the data center heat exhaust air conditioning energy consumption down. We feel that in accordance with the current majority of ways to compare, it is possible to achieve energy savings of more than 70% of the air conditioning of the server room, equivalent to the server room to reduce electricity consumption by more than 30%. Just now I heard the leader say, foreign developed countries than, computer room PUE to 1.2, 1.3 that has a relationship with the location of its computer room. In different climatic conditions, in fact, grasp these several, mainly natural cold source, appropriate plus a little mechanical refrigeration supplement to solve the year inside 20%, 25% of the energy saving, can be completely different places in our country's data centers air conditioning energy consumption are effective down, should be done better than the developed countries than the United States, thank you.